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Old 01-08-2022, 01:33 PM   #1
84B23F
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Default Rex-Regina IAC (1389557)

The scalpers are selling used IACs for $200 to $350, and mine shot craps on 1993-940.

Cheap and quick cold weather solution: 93-940

1. Unplug TPS's plug, and IAC's plug.

2. In park with a warmed up engine, set idle to 1,000 RPM via throttle-body's idle set screw.

Nut will have to be backed off, then apply some WD-40 to screw, wait, then turn set screw with small plain screw driver, then tighten nut down. I had to increase RPM. YMMV...depends upon how much air IAC is passing.

In cold weather when starting, foot throttle will have to be applied a pinch to keep engine from stalling. Currently, I'm not sure how much extra air is required for a cold start to keep engine running, but this part, Dorman 600-104, when hooked to an intake vacuum port on one side, might allow enough air to keep engine running after a cold start. Different ways to energize this Actuator Valve

Last edited by 84B23F; 01-10-2022 at 10:59 PM.. Reason: Revised
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Old 01-14-2022, 11:45 AM   #2
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Can’t you just use a Bosch IAC & it’s rubber holder (& maybe you need the hoses from the LH redblock too I forget it’s been a while since I’ve done the LH idle motor to replace defective VDO idle motor on regina 7/9 dance?) from an LH2.4/3.1/ -‘98 850/70 series, SAAB C900or random VW/Audi & some bmw Teutonic Bosch FI eurotrash donor car of that ~’89-‘98 pre e-throttle vintage with that 2-pin form factor IAC with compatible coil reistance/internal valve guts/orifice side that mostly seem to work ‘fine’ / no fuss?

You’re a resourceful industrious wily old-hand cheapskate vintage Volvo buzzard hack/shade tree Kansan/okie, you’ll figure this out somehow or other with some sort of whathaveyou fook-in , i have faith

The original VDO idle motors were kinda cheap bean-counter defective junk on the regina cars…hunting idle/lazy delayed response or ‘sticky’ from near new off the dealership floor particularly evident / notable in very cold starts…
…final revision/ version of the ECU (1993 940 in the USA market?) & LH IAC retrofit, no more BS/drama if I remember well/didn’t get paid to fix that many regina 7/9s…

Updated with some less bean counter cheap components, the Regina’s actually pretty reliable & kinda more fuss-free than the Bosch LH even in some ways?
Does yours have the tiny fuel pressure regulator instead of the Bosch LH style rail and FPR/regulator?
Remembering installing a random used junkyard fuel pump outta some random Honda/Toyota...no more BS / cheap GM bean counter single pump drama!
Cheap GM & eurotrash bottom of the barrel bean-counter junk….swap some of that stuff out for quality compatible parts, no more BS is all remember with the Regina?

I forget what junkyard car I got some Bosch Gen 3 injectors off of & a better 02 sensor off of that’s quality/lasts well no fuss and cleaned with a stainless brush & some white gas.
Most of the regina or redblock cars are good & dead by now
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Old 01-14-2022, 03:23 PM   #3
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You may be able to use a LH2.4 IAC per: https://www.brickboard.com/RWD/index...299&show_all=1

Note: the LH2.4 IAC is a little strange in that the unconnected (fully off) position of the air shutter is slightly open to allow a limp mode. As the shutter rotates, as more electrical power is applied, the valve goes from slightly open (limp), to shut, back to slightly open, and then on to fully open. Can you look at the old Regina valve and see if it's slightly open with no power?

TP31361 (ozvolvo.org/archive/) shows sketches of the LH2.4 valve operation, including a limp mode adjustment screw (epoxied over).
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Old 01-14-2022, 07:56 PM   #4
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Originally Posted by Kjets On a Plane View Post
Can’t you just use a Bosch IAC
Internet scans suggest IACs have Hz-Range/pulse duration/current draw, like fuel injectors. Then MegaSquirt FAQ mentions amount of current draw is dependent upon which IAC is being used, and IACs are designed for a specific frequency range (Hz), so several issues should be considered before flipping...never seen a spec sheet.

In later carburettor days for US OEM carbs, hot idle could be adjusted, which I did on 940, and cold start idle would drop as engine warmed up (or via electric heating element). Essentially, there was a fast idle when cold, and fixed idle position when hot. So, the throttle plate's position determined how much air goes into air intake.

With an IAC, you don't move the throttle plate to increase RPM, the IAC just adds more/less air to maintain RPM in cold/hot conditions.

When I get this part next week, Dorman 600-104, I believe its vacuum designed circuit is closed until voltage energizes it. I'll be using it for air to pass into intake manifold, which will increase engine RPM to a fixed value for a given cold engine temperature when starting.

When a warm day exists, I'll tinker with it; in essence, you don't need an IAC if hot idle is adjusted to a fixed RPM, and for cold idle, you either use your right foot to control cold idle, or maybe get that Dorman 600-104 part, and rig up an on/off means.

On/Off means might be via vehicle's high beam power, AC compressor hot wire, dash fog-light switch, etc. I don't think Dorman 600-104's solenoid would use much current (amp).

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Old 01-14-2022, 08:20 PM   #5
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Originally Posted by bobxyz View Post
You may be able to use a LH2.4 IAC per:
Thx...current draw would be my chief concern...internet scans suggest if ECM/IAC's frequency range is not similar, buzzing may happen, and ECM may not get idle correct...overshooting/undershooting RPM. Note - Pulse width may be related also.

Quote:
Can you look at the old Regina valve and see if it's slightly open with no power?
Either closed or a pinch open...with throttle plate to factory specs, hot engine will die at idle. Assuming IAC is within dimensional "air" specs with power off (unplugged). I don't plan to remove it currently, but I plan to evaluate Hz/pulse-width at a later time. Too Cold now!
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Old 01-14-2022, 11:15 PM   #6
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I chucked the old Regina VDO & installed the Bosch LH2.4 IAC, car stopped hunting & ran fine for the last ~15 years?
Maybe it'll fry the $1000 (when new) probably NLA regina ECU & your electronics concerns are totally legit/valid, but so far, so good, no more hunting or sticking cold/seemed to really improve things over that cheap VDO that sticks or has the windings short out?

You can fold the tabs, open the IAC up on most of them to examine it & calculate the reflected moment of inertia, orifice size & wire size/total windings if you got time on your hands & an ocilliscope/electronics fine instruments/tools to poke & prod it...

I also chucked the regina FPR & installed the Bosch fuel rail/FPR, no more bull****, much better longevity/parts availability, thereafter.

Chucked the GM cheap crap in-tank pump & just stuck a random camry V6 single tank pump in there...no more BS/never seen one go bad on a toyota that wasn't run out of gas or flooded or got a really bad batch of fuel/clogged the sock/strainer or seized the pump?

Do that & use the Bosch Gen 3 clean injectors/some decent pintle caps & replacement quality o-rings & clean a decent compatible 02 sensor & use the updated last version 1993 regina ECU & they seem to run pretty good/efficiently without excessive engine or FI component wear/no fuss?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can recombine the junkpile in uh...various ways on the Volvo to control the idle with factory hoses/parts that all have OEM fit:

-Use the constant idling system from LH1.0 cars w/EFI intake manifold w/ constant idling system ECU, 3-wire idle motor, 2-wire coolant temp sensor thermistor & vacuum switch on the firewall to trigger idle control/fuel cut (no TPS or micro-switch on the LH1.0 cars) as the LH1.0 cars did or use the TPS idling contact for the micro-switch function on 240Turbos or K-jet cars w/constant idling system (CIS).

-Use the valve (cam?) cover mounted idle slide/sluice used on various fuel injection models. It has a heating element in it that's powered as soon as the engine is turning/fuel system relay's switched on to slowly close down (it's adjustable for cold idling opening size). Cars with A/C had a simple 12V A/C idle-up solenoid screwed into the throttle body bypass port when the A/C relay was energized (IIRC energizes the idle-up solenoid to raise idlig the entire time the rotary dial's turned, not just the with the compressor clutch...makes sense, don't want a stall when the compressor cuts in at idle under heavy load in hot weather).

In practice with the heated bi-metallic spring cam cover mounted cold fast-idle air slide/sluice, unless the airbox t-stat works perfectly & preheat tube's connected & belly pan's in place & seals well, in cold weather, unless you block off the radiator to keep extremely cold air out of the engine bay or shut the engine off &/or let the engine bay heat soak at the first stop sign ~1/4 mi up the road w/the coolant up to temp for a minute or two, it's hard to get it to settle down & stop fast idling.
Also, likewise, in extreme heat with lots of heat soak, with only air/no coolant reference, it can also stall out/close down a bit too much, in my experience, but the spec isn't that precise; 700-1150 is the 'warm' idling spec on a lot of B21Fs for example without the constant idling system.
That's about the *best* case scenario, but the thing does work as designed/within that idling spec, broadly, if you block off the grill/radiator in extreme cold & preheat/airbox T-stat wax pellet works & engine cooling fan clutch works to prevent heat soak...

But you're broadly correct, & it's better to fast idle & run leaner on first cold startup, tho not too fast shearing the oil, but you don't want the engine to flood/foul or die in extreme cold or to run real rich for too long & wash down the oil or cause premature wear.
In theory, the constant idling system ECU (some of the VW/Audi are adjustable for cold & hot idling speed) idles faster with colder coolant temp, tho the variation in practice isn't all that much; ~1050-1100rpm in extreme cold & the usual ~850-900RPM hot.

I wouldn't know about installing any chinesium 'parts store' domestic car crap on volvos, but we have Volvos & yuppie eurotrash cars same vintage as the RWD Volvos, generally, still (slowly) trickling in our junkyards...kinda...tho who knows for how much longer? Waste not, want not, eh?

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Old 01-15-2022, 03:48 AM   #7
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.






Here's the only specs I could find locally (from TP31903_1 ReginaBook.PDF)

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Old 01-15-2022, 04:00 PM   #8
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You may be able to use a LH2.4 IAC per: https://www.brickboard.com/RWD/index...299&show_all=1

...
Regarding that link, I did spend another summer afternoon playing with those Regina idle valves using the 100 Hz rate Bosch uses. I'll search for my notes from 8 years ago, but the one thing I do remember was thinking "what a piece of crap." It wasn't "eurotrash" but like some way to get around a patent maybe Bosch owned. Anyhow I don't believe there's any chance you'll harm that Siemens ECU connecting the Bosch valve, and given the limp-home rest opening it will provide that bit of fail-safe stall on the RR tracks air I'm not sure the VDO valve provides.

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Old 01-15-2022, 04:28 PM   #9
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Originally Posted by Kjets On a Plane View Post
Regina VDO...sticks or has the windings short out?
Coming back on a 360 mile road trip, I lost full power in last 15 miles or so, and running around 40 mph max.

I believe the IAC was stuck in the full open position, so that when the pedal was depressed further, engine acted like it was starved for fuel...jerking motions.

ECU's (Regina) fuel table, I assume has Max/Min fuel limits at various RPMs, and with IAC fully opened, and throttle at "its" normal position for a given speed, too much air was entering the intake, which caused the jerking motions. RPMs over 2,000 would bring about fuel starvation motions; ran fine under 2,000 RPM under light load conditions (flatish roadways).

>Bosch LH2.4 IAC

Will consider...thanks...but so far, I don't need an IAC with hot idle RPM set to 1,000. When starting in minus temps, I let it fire up, and then apply a little throttle...bring RPM back to around 1,000, and shift into Drive...then drive on for seven miles before coming to a stop.
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Old 01-15-2022, 04:35 PM   #10
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Originally Posted by cleanflametrap View Post
limp-home rest opening
On one local trip, I had to keep accelerator peddle slightly depressed when stopped to prevent engine from stalling out. So, I adjusted the hot idle RPM to 1,000 RPM, and disconnected IAC and TPS; that problem was then solved.
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Old 01-15-2022, 05:56 PM   #11
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It needs pics/diagrams (‘worth 1000 words’) , outline & fine tooth comb abridged version, for sure.

But it has *any* formatting.
It gives a bit of shared experience getting those bean-counter components out of your Regina car to get it to work reliably and if you want a basic cold fast idle idle bypass w/o electronic control, it gives a suggestion & experience re that recombining the OEM Volvo/Bosch FI junkpile, or separate/stand-alone CIS system for idle control only & let the ecu or Bosch breakerless (or EMS if your choosing?) do the fuel/spark only, if that’s what you want?

It’s just experience, I don’t have the ‘circuit brain’ Art & Bob(xyz?) does for theory & testing/poking & prodding with fine(r) electrical instruments on a sunny day with beer with pictures & detailed captions…

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Old 01-15-2022, 06:11 PM   #12
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Is there any chance there's a cheaper GM branded part it crosses to?
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Old 01-15-2022, 06:33 PM   #13
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Originally Posted by cleanflametrap View Post
Siemens ECU....Bosch valve...limp-home rest opening
Speculation Footnote - Inward side of exhaust tailpipe is darker in color recently, either due to O2 sensor, or Regina not controlling the IAC.

Short story short, I believe Regina controls full time the IAC when engine is running. All the TPS does is informs Regina about idle or full throttle positions...just used as an idle RPM setpoint to be maintained.

I rebuilt the 1984B23F engine, and its not an oil burner: O2 sensor was replaced awhile back, so my guess is Regina finely tunes air/fuel mixture via IAC. Regina uses MAP sensor, and Bosch uses AMM (MAF), so AMM knows amount of air flow, and Regina used MAP/O2 to fine tune fuel/air mixture.
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Old 01-15-2022, 06:41 PM   #14
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Is there any chance there's a cheaper GM branded part it crosses to?
As we said when we had a Toyota T-100 4-cylinder & various GM offerings in the landscape light duty truck fleet ‘GM parts are (often) cheap, but not necessarily Inexpensive.’

Idk where that balance is with the Siemens / Bendix FI between cheap/cross references to a bunch of compatible GM domestic junk ubiquitously @ parts store / counter 4 ¢h33p (but it'll likely fail again in 2-5 years & leave you stranded/right back at the parts counter on short notice being cheap junk?)
vs.
pull something compatible electrically off of a Bosch FI Volvo or tank pump out of an Asian car used that might last you until you die or rusts out/gets wrecked if the used part is properly evaluated prior to install & installed & given proper care & feeding thereafter?

My conservationist side heavily biased to the latter (partly by circumstance/proximity between Bay Area/land of the notorious BIG & Sleazattle w/1970s-1990s eurotrash self-serve junkyard cars (relatively) abundant (I'm a creature of habitat as much as the next guy)) says never buy any inferior quality anything new or give the corporation any $ for their defective planned obsolescence slave labor crap for cars out of 10 year federal implied / extended chassis warranties / lemon laws or out of stringent quality control of high production volume runs current models, but in practical terms it’s not always possible to finely evaluate & poke & prod & keep it all junkyard/used & all 1998 & earlier on the Volvos without that being a full time job &/or max scientist’s persuit &/or religious fanatic’s / army of 1s life…so I’m finding…

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Old 01-16-2022, 10:04 AM   #15
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Good to wean from all this that the LH2.4 IACV can be dropped in with just connector/hose swap. I hadn't considered that option. My Regina/Rex +T still has the appropriate cold start, idle & warm values with the Regina IACV, however I have a bucket of LH2.4 IACV's vs. no spare Regina versions...
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Old 01-16-2022, 11:21 PM   #16
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LH2.4 IAC>>>>Regina/Rex .
When a new LH 2.4 IAC arrives, and if weather is warmer, I'll do an oscilloscope test and see what idle Hz and pulse width are, and if they change with RPM.

Based upon my driving experience, I suspect Regina uses IAC full time; somehow, I think the IAC was in a stuck open position when driving highway miles.
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Old 01-17-2022, 01:53 PM   #17
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Coming back on a 360 mile road trip, I lost full power in last 15 miles or so, and running around 40 mph max.

I believe the IAC was stuck in the full open position, so that when the pedal was depressed further, engine acted like it was starved for fuel...jerking motions.

ECU's (Regina) fuel table, I assume has Max/Min fuel limits at various RPMs, and with IAC fully opened, and throttle at "its" normal position for a given speed, too much air was entering the intake, which caused the jerking motions. RPMs over 2,000 would bring about fuel starvation motions; ran fine under 2,000 RPM under light load conditions (flatish roadways).
I'd guess that a sensor was acting up and you were experiencing some sort of limp mode. Were there any diag codes posted?

The Regina MAP sensor doesn't care where the air is coming from -- idle valve, throttle, valve, gasket leak are all the same, and the TPS is a simple idle switch and WOT switch. So, for a given MAP reading and IntakeAirTemperature, Regina looks up the base injector pulsewidth for the desired AFR (i.e. it adjusts the fuel to match the measured air, wherever that air came from).

For the LH2.4 IAC, the coil resistance is listed as 8 ohms. The LH2.4 ECU or Regina ECU grounds one side of the IAC to energize it. With 12volts across the coil, a LH IAC draws 1.5 amps, and the 4 ohm Regina IAC draws 3 amps. Pulse width modulation reduces the average current. Connecting a LH IAC to a Regina ECU won't hurt it (draws only 1.5 amps while it was designed for 3 amps). Connecting a Regina IAC to a LH ECU may hurt it (2x the current it was designed for).

I asked about the no power IAC limp opening because the control algorithm needs to know about it for best operation. I'd guess that the LH ECU simply sets the minimum IAC PWM % to 20%, or something similar, to ensure that the IAC is operating in the normal (non-limp) range of rotation. Even if the Regina IAC doesn't have the special no-power limp opening, the control algorithm may still work -- it would keep increasing IAC PW% until it gets into the linear (non-limp) range of the IAC barrel rotation.

LH2.4 keeps the IAC open at all times and adjusts the opening up and down as the rpm/load change. It also bumps up the IAC by ~5% when the A/C kicks on (not shown below). LH2.4 runs the IAC PWM at 97.6Hz (or 1 / 10.240ms).

Here's a graph of LH2.4 IAC PW% (bottom white line) in operation over ~10 minutes of my drive to work (click pic for bigger):


If you have a spare LH2.4 IAC valve around, I'd say to give it a try. It may not respond as smoothly as the original IAC (either slow to adjust or hunting idle), but should give a better idle over a broader range of conditions than simple on/off valves.

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Old 01-17-2022, 02:47 PM   #18
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Were there any diag codes posted?
I'll check when installing a LH 2.4 IAC; rarely do I check for a code...old school, just fix what I think is wrong.

Many thanks for tidbits...

RE: cleanflametrap

Regina does have this code...and I perceived this was happening, which is why I readjusted throttle plate to allow more air for increasing RPM to 1,000.

233 - Idle valve closed/possible air leakage
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Old 01-17-2022, 05:34 PM   #19
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Regina MAP...IntakeAirTemperature, Regina looks up the base injector pulsewidth for the desired AFR
Regina may have a Speed Density setup, which was used in earlier days by GM when their MAFs screwed the pooch on Berettas. If true, calculations would be based upon revolutions per minute times displacement.
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Old 01-17-2022, 07:10 PM   #20
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Yes, Regina is speed-density, like MegaSquirt and other ECUs that use a MAP sensor instead of a MAF sensor. While the fueling is proportional to RPM, this term drops out when the ECU is setup to do 1 squirt per rev, or per 2 revs - as RPM goes up, cc of fuel per minute automatically goes up to match. Details of the MegaSquirt speed density fueling equation can be found here
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Old 01-18-2022, 12:51 AM   #21
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I wonder if it retards the ignition timing/similar if the IACV doesn't close properly to prevent a racing engine or runs some kind of limp mode w/ the regina ECU?

Bad IACV on the regina cars has *usually* presented as more of a hunting or stalling cold idle for me YMMV?

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Old 01-18-2022, 08:50 AM   #22
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Quote:
Originally Posted by bobxyz View Post
While the fueling is proportional to RPM....
A fully opened IAC allows more air than a closed IAC, for a given throttle plate position

Code 233 - Idle valve closed/possible air leakage (just taken from Regina tech writeup, which suggests Regina knows if this is not functioning).

I understand the concepts, but not specific ECM programming, and how it executes. The MAP would be fully "aware" but perhaps fuel RPM table and Map's may not be on the same page when ECM assumes IAC is in some programmed position.

Again, 2,000 and below RPMs were OK with partial throttle pedal positions were used; after setting hot idle to 1,000 RPM, and disconnecting TPS/IAC, this issue went away.

Hot idle at 1000 RPM, so when coming to a stop, or shifting into Park, idle RPM may be a pinch higher, but it slowly comes back to 1000...I assume O2 adjusting fuel amounts.

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Old 01-22-2022, 07:45 PM   #23
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old Regina valve
0 Volt - Closed so no air passes thru

>LH2.4 IAC
1. (fully off)..slightly open to allow a limp mode.
2. power...goes from slightly open (limp), to shut, back to slightly open,
3. and then on to fully open.

I don't know if LH 2.4 requires correct polarity, but hot engine died with no pedal action when starting (limp>shut), then mostly hovered around 1,000 RPM when driving with check engine light on. Once, RPM dropped to kill engine when stopped, and once way low in town, so I pressed throttle pedal down a pinch. Throttle plate was setup to allow some 700 RPM when LH2.4 was plumbed in.

When electrical plugs (TPS/IAC) are detached, check engine light will be gone on a restart.

With a cold start, Regina should increase pulse width, but I suspect I'll be removing that new IAC and put it on a 240 of mine. 940 is sitting now, waiting for a new tire, so within a week, I'll take another look. I have no idea if Regina can learn and store info for open/closed loop.
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